Science
Reps in Reserve (RIR)
RIR is a way to autoregulate training intensity without percentage charts — you rate how many reps you had left in the tank, and let that number steer your working weights session to session.
What the evidence says
Reps in Reserve (RIR) is a self-reported scale that describes how many reps you could have completed after stopping a set. 0 RIR means you went to failure; 3 RIR means you stopped three reps before failure. It is a practical tool for autoregulating training intensity without the rigid constraints of percentage-based programming.
Percentage-based programming (e.g., 75% of 1RM for 3×8) assumes your 1RM is stable, accurately known, and that the prescribed percentage represents the same relative effort every day. Neither assumption holds in practice: daily readiness fluctuates, 1RM estimates drift, and recovery between sessions varies. RIR adjusts automatically — if 225 lb feels like 3 RIR on a good day and 0 RIR on a bad one, you train the right intensity both days without changing the number on the bar.
Studies by Eric Helms et al. show that lifters with 2 or more years of training can self-report RIR with reasonable accuracy — within 1–2 reps of actual failure on most sets. Beginners are less accurate but improve with practice. The error margin shrinks when lifters take sets closer to failure: at 0–1 RIR, people reliably know they are near failure; at 5 or more RIR, estimates become less precise.
LiftProof logs RIR alongside each set. The app uses logged RIR across sessions to identify trends — if your RIR is drifting down on the same weight over multiple weeks, it signals either accumulated fatigue or that your training max needs recalibrating upward. RIR is the primary autoregulation signal in LiftProof's programming logic.
Evidence base
Sources
Source 01
Helms et al. 2016 — RPE and RIR as autoregulation tools(opens in a new tab)Examines accuracy of RPE/RIR self-reporting in trained lifters.
Source 02
Zourdos et al. 2016 — Novel Resistance Training–Specific RPE Scale(opens in a new tab)Introduces the 1–10 RPE scale for resistance training, which maps directly to RIR.
Source 03
Mike Tuchscherer — The Reactive Training Manual(opens in a new tab)Foundational text for RIR/RPE-based autoregulation in powerlifting.
LiftProof defaults draw from the published strength literature.